For the validation of a new beam element formulation, a wide set of experimental
data consisting of deformation patterns obtained for a number of specially
designed composite beam elements, have been obtained. The composite materials
applied in the beams consist of glass-fiber reinforced plastic with specially
designed layup configurations promoting advanced coupling behavior. Furthermore,
the beams are designed with different cross-section shapes. The data obtained
from the experiments are also used in order to improve the general understanding
related to practical implementation of mechanisms of elastic couplings due to
anisotropic properties of composite materials. The knowledge gained from these
experiments is therefore essential in order to facilitate an implementation of
passive control in future large wind turbine blades.

A test setup based on a four-column MTS servo-hydraulic testing machine with a
maximum capacity of 100 kN was developed, see Figure 1. The setup allows
installing and testing beams of different cross-sections applying load cases
such as axial extension, shear force bending, pure bending in two principal
directions as well as pure torsion, see Figure 2. In order to apply multi-axial
loading, a load application system consisting of three hydraulic actuators were
mounted in two planes using multi-axial servo-hydraulic control. The actuator
setup consists of the main actuator on the servo-hydraulic test machine working
in the vertical axis (depicted on Figure 1) placed at the testing machine
crosshead and used for application of vertical forces to the specimens. Two
extra actuators are placed in a horizontal plane on the T-slot table of the test
machine in different positions in order to apply loading at the tip of the
specimen in various configurations.

In order to precisely characterize the global as well as surface deformations of
the beam specimens tested, a combination of different measurement systems were
used during the tests. Digital Image Correlation (DIC) systems [1] able to
measure the 3D displacement field along the specimen surface were applied. Two
linked DIC systems were used simultaneously during the experiments in order to
obtain measurements for most of the surface of the beams. Additionally, an
optical system based on mirrors and laser beams allowing direct measuring of the
twist along the specimen were applied as well. Results from both systems were
additionally used to verify obtained results.

A number of FE models with different modeling approaches were furthermore
developed for each specimen type and validated against the experimental results.
The models were also used to investigate inaccurate prediction of torsional
behavior of composite structures when utilizing nodal offsets in shell element
based models [2, 3].

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